数据库 PCC OCC

For isolation characteristic of transaction management in database, two mechanisms are used: PCC and OCC.
PCC(Pessimistic Concurrency Control): get lock before access;
application: competitive race conditions; or when the cost of lock protection is lower than that of rollback
OCC(Optimistic Concurrency Control): read, check and write
application: less competitive race conditions; or when the cost of occasional rollback is lower than that of consistent lock